Nowadays, by virtue of their superior magnetic properties, rare earth sintered magnets, typically neodymium and samarium-based magnets are widely used in motors, sensors and other devices to be mounted in hard disks, air conditioners, hybrid vehicles, and the like. In the automobile field, for instance, severe fuel consumption regulations are enforced in many countries under consideration of global environmental problems. As the solution, the development and use of hybrid cars capable of reducing the load of internal combustion engines is accelerated and widespread, and electric auxiliaries for electric power steering systems and electric oil pumps also become widespread. Electric motors for use in these applications must meet the requirements of low profile, light weight, and high performance. Nd and Sm-base sintered magnets are frequently used because of their superior properties.
These motors are recently required to further improve their performance. For the purpose of efficiency improvement, in many cases, sintered magnet blocks are divided into magnet pieces of small size, which are mounted in place. For the production of such divided magnet pieces of small size, a method of furnishing a magnet block of large size as starting stock and cutting the block into a multiplicity of magnet pieces is efficient. The known cutting means include multiple outer-diameter (OD) blades and multiple wire saws. In either case, in order to prevent magnet alloy chips from scattering and to ensure an accuracy of cut size, most methods and apparatus for cutting magnet alloy blocks are of batchwise production mode in that a sintered magnet block is cut into a multiplicity of pieces while the block is fixedly secured to a cutting jig by means of a clamp mechanism.
Referring to FIG. 8, a prior art apparatus including multiple OD blades is illustrated. A plurality of magnet blocks 1 are adhesively secured to a carbon jig 101, which is mounted on a slide table 102. The jig 101 is moved in the arrow direction at a predetermined speed while multiple OD blades 2 (six blades in the figure) are rotated in the arrow direction. The magnet blocks 1 together with the carbon jig 101 are continuously cutoff machined by the rotating blades 2. In this way, one magnet block is divided into a multiplicity of magnet pieces (five pieces in the figure).
This method for cutoff machining magnet blocks is described in detail. First a solid wax (e.g., Adfix series wax by Nikka Seiko Co., Ltd.) is melted by heating at a predetermined temperature and applied to the carbon jig 101. A plurality of magnet blocks 1 (twenty blocks in the figure) are arranged in cascade and adhesively secured to the carbon jig 101. The jig 101 is mounted on the slide table 102. At this point, the jig 101 is accurately positioned and fixedly secured by inserting spacers 103 and tightening three screws 104.
In this state, the slide table 102 is moved in the arrow direction, the multiple OD blades 2 are rotated at a high speed, and a coolant is supplied to the cutting site from a coolant supply nozzle 3. Each magnet block 1 is cutoff machined together with the carbon jig 101 surface by the rotating blades 2. One magnet block 1 is divided into five magnet pieces 11. After the completion of cutoff machining, the cutting apparatus is interrupted, the screws 104 are loosened, the carbon jig 101 is dismounted, the jig is heated again to melt the wax, and the magnet pieces 11 are removed from the jig 101. After cleaning with an organic solvent at elevated temperature and hot air drying, the magnet pieces 11 are recovered. Once any wax deposit remaining on the magnet-bonding surface of the jig is removed, the carbon jig 101 is ready for reuse, that is, subjected to the cutting operation again after new magnet blocks 1 are adhesively secured thereto. By repeating the cutting operation, magnet blocks 1 are cut into magnet pieces.
The batchwise production method mentioned above, however, involves appurtenant steps, setups and changeovers such as setting of magnet blocks in the jig, mounting and dismounting of the jig, heating and cleaning with organic solvent, which cause significant drops of operating capacity and productivity.